[RFC PATCH bpf-next 06/12] bpf: Add prog_list_init_item(), prog_list_replace_item(), and prog_list_id()

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Martin KaFai Lau <martin.lau@kernel.org>

Add three helpers to abstract operations on a bpf_prog_list entry.

Right now, bpf_prog_array_item is initialized from prog_list_prog(pl),
which returns either pl->prog or pl->link->link.prog. This will not work
when struct_ops is attached to a cgroup because the attachment is backed
by a struct_ops map instead of a BPF prog.

The same applies to __cgroup_bpf_query(). Instead of always copying a
prog id to userspace, struct_ops cgroup attachment will need to copy the
struct_ops map id.

Refactor bpf_prog_array_item initialization into prog_list_init_item()
and prog_list_replace_item(), and refactor id lookup into prog_list_id().
These helpers will be extended to support pl->link->map in a later patch.

This is a no-op change.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
 kernel/bpf/cgroup.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index abfd6df349d4..720eaa3285a2 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -378,6 +378,22 @@ static struct bpf_prog *prog_list_prog(struct bpf_prog_list *pl)
 	return NULL;
 }
 
+static void prog_list_init_item(struct bpf_prog_list *pl, struct bpf_prog_array_item *item)
+{
+	item->prog = prog_list_prog(pl);
+	bpf_cgroup_storages_assign(item->cgroup_storage, pl->storage);
+}
+
+static void prog_list_replace_item(struct bpf_prog_list *pl, struct bpf_prog_array_item *item)
+{
+	WRITE_ONCE(item->prog, pl->link->link.prog);
+}
+
+static u32 prog_list_id(struct bpf_prog_list *pl)
+{
+	return prog_list_prog(pl)->aux->id;
+}
+
 /* count number of elements in the list.
  * it's slow but the list cannot be long
  */
@@ -471,9 +487,7 @@ static int compute_effective_progs(struct cgroup *cgrp,
 				item = &progs->items[fstart];
 				fstart++;
 			}
-			item->prog = prog_list_prog(pl);
-			bpf_cgroup_storages_assign(item->cgroup_storage,
-						   pl->storage);
+			prog_list_init_item(pl, item);
 			cnt++;
 		}
 
@@ -957,7 +971,7 @@ static void replace_effective_prog(struct cgroup *cgrp,
 				desc->bpf.effective[atype],
 				lockdep_is_held(&cgroup_mutex));
 		item = &progs->items[pos];
-		WRITE_ONCE(item->prog, link->link.prog);
+		prog_list_replace_item(pl, item);
 	}
 }
 
@@ -1275,15 +1289,13 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
 		} else {
 			struct hlist_head *progs;
 			struct bpf_prog_list *pl;
-			struct bpf_prog *prog;
 			u32 id;
 
 			progs = &cgrp->bpf.progs[atype];
 			cnt = min_t(int, prog_list_length(progs, NULL), total_cnt);
 			i = 0;
 			hlist_for_each_entry(pl, progs, node) {
-				prog = prog_list_prog(pl);
-				id = prog->aux->id;
+				id = prog_list_id(pl);
 				if (copy_to_user(prog_ids + i, &id, sizeof(id)))
 					return -EFAULT;
 				if (++i == cnt)
-- 
2.53.0-Meta